DRAM Timing mode (quick question)

You know in your BIOs, under the memory settings, they have a setting "DRAM Timing Mode" (at least that's what its called in my BIOs) With the options "DCT0", "DCT1", "Auto" and "Both"

Well I am aware it is supposed to be set on both, but when it is set on both, they give you two of everything (TCL, TRCD, TRP, TRAS, TRC etc) Are you supposed to set them BOTH to the preferred settings or just set one set?